A frontal vehicle impact can rapidly decelerate a vehicle. Vehicle occupants, to the extent they are not rigidly restrained and are able to move within the vehicle, do not decelerate in synchronicity with the vehicle. The momentum of the occupants causes them to continue to move forward relative to the vehicle during a rapid deceleration of the vehicle. When an occupant is partially restrained by a conventional three-point seat belt system including a lap belt and a shoulder belt, it may still be possible for the occupant's thighs and pelvis to slide forward. Such forward motion has been characterized as submarining, as the occupant's thighs and sometimes their pelvis slide under the vehicle's dashboard.